Rivets of the type which include a rivet body and a mandrel are referred to as pull or blind rivets. In the setting operation of these rivets they are inserted into the components to be joined, the mandrel is gripped, pulled axially, and its head upsets the rivet body forming a blind head. These rivets are well-known in the art and are further described, for example, in commonly-assigned DiMaio U.S. Pat. No. 3,374,656.
Blind rivets may be set, pulled or rivetted by tools powered by compressed air, hydraulic means, mechanical arrangements or combinations thereof.
Tools powered by compressed air piston which are mechanically connected to the mandrel pulling mechanism have been suggested in the art. For example, it has been suggested to pneumatically power a piston which is connected to a pivoted linkage which in turn is connected to the mandrel pulling mechanism. The pivoted linkage accomplishes a mechanical advantage in that the pulling mechanism moves through a lesser distance than the piston. Such prior mechanisms have, however, lacked success in that the mechanical advantage of the linkage is reduced as the power stroke nears its completion.
Other tools, have used springs to accomplish the return stroke thus requiring that the spring force be overcome during the power stroke and reducing the effective pulling force of the tool.
The present invention provides a mechanical linkage which maintains an undiminished mechanical advantage between the rivet pulling assembly and the piston and rod unit throughout the power stroke. In addition, the present invention provides a new and useful way of controlling the air pressure to effect the operation of the tool during both power and return strokes.